It is well known that stabilizers are used in well drilling to aid in drilling direction holes, to aid in drilling a straight hole and to prevent contact between the drill string and the bore hole. In the past, the stabilizers were made up within the drill string as the string was run into the hole; however, this arrangement has several undesirable aspects because it adds tool joint connections to the drill string, which increases possible points of failure in the drill string, causes variations in drill collar stands which increases trip time and unsafe operation for rig personnel, requires a special bottom hole assembly which increases drilling costs, and does not permit adjustment of the stabilizer along the drill string without changing stubs which increases drilling costs.
The use of lock-on stabilizers has been suggested to solve these undesirable aspects. Typically, the lock-on stabilizer has a body with externally extending blades, two end caps for connecting to the body, an inside solid locking ring and two outside solid locking rings with a single tapered surface for each ring. The stabilizer is connected between pin and box joints on the drill string by positioning the inside locking ring inside the body, positioning an outside locking ring on either end of and with the tapered surface facing the inside locking ring. Two end caps are used to force the rings together within the body to connect the stabilizer to the drill string. A major difficulty with this arrangement has been its inability to be reused after once being attached. This difficulty is caused by the inherent inability of the solid locking rings to clamp around the drill string without being deformed.
It is also well known that the externally extending blades wear rapidly and break when drilling through abrasive earth formations and when contacting casing. This breakage can prevent the drilling mud from passing on the return trip to the surface, which forces a replacement of the stabilizer. This replacement of course takes time and is expensive.
It is, therefore, an object of this invention to provide a stabilizer that is rapidly and easily releasably connected to a drill string for adjustable positioning along the drill string.
It is a further object of this invention to provide a drill string stabilizer with easily replaceable externally extending blades.
Moreover, an object of the present invention is to provide a stabilizer of simple and inexpensive construction which is releasably connected to a drill string.
In accordance with the invention, a releasable stabilizer is provided for adjustable positioning along a drill string. The stabilizer has a body for positioning around the drill string having female threads at each end of the body on the interior surface, a tapered portion of the interior surface extending outwardly to the female threads and blades extending from the exterior surface of the body to contact the bore hole. An end cap is provided for each end of the body and has male threads at one end of the exterior surface and a tapered portion of the interior surface extending outwardly toward the end with the male threads. At least one clamping wedge is used for each of the body and has a surface formed by first and second tapered portions, the first tapered portion tapering in a direction opposite to the taper of the second tapered portion. Each clamping wedge also has a gripping surface for moving into contact with and gripping the drill string by positioning the surface of the first tapered portion of said clamping wedge against the interior surface tapered portion of said body and threadably connecting said end cap to said body, which causes the interior surface tapered portion of said end cap to move against the surface of the second tapered portion of said clamping wedge for ultimately attaching the stabilizer onto the drill string.